1. Field of the Invention
The present invention relates generally to the field of power controller apparatus for electrical and electronic equipment, and more particularly to time delay power controller apparatus for such equipment.
2. Discussion of the Prior Art
It is well known by electrical engineers and most users of electrical of electronic equipment that when a piece of such equipment is turned on, a high turn-on electric current is caused in the equipment. Within several seconds, usually less than about 2-4 seconds, the turn-on current spike decays to a steady state, operating current. The turn-on current spike is caused by the charging of cooperative elements or portions of the equipment and is dependent upon the rate of electrical charging of the equipment, as given by the differential equation: EQU I=dQ/dt,
wherein I is the current and dQ/dt is the time rate of charging.
From the above equation it can be seen that a fast equipment turn-on, in which dQ/dt is high, gives rise to a high current spike. Typically, the turn-on current spike is several times higher than the steady state or average current drawn by the equipment subsequent to turn-on.
The combined effect of individual high turn-on currents of each of several or a number of pieces of electrical or electronic equipment is that the current carrying capacity of existing building electrical circuits into which the equipment is connected may be exceeded. This then causes circuit breakers to trip open at the instant the equipment is turned on, thereby shutting down all the equipment. This may occur even though the building circuit may have capability for safely handling the combined steady state operating currents of the equipment.
In some instances where several different building electrical circuits are conveniently available, the possibility of overloading individual ones of the building circuits may be avoided by connecting different pieces of equipment into separate circuits. However, a multiplicity of separate building circuits is typically not available in a single room where a number of pieces of electrical or electronic equipment, for example, a computer and several associated disc drives, are located. The installation of several independent building circuits to service several pieces of electrical equipment may be very costly.
Although sometimes possible to do so, it is generally not feasible to substantially reduce turn-on current spikes by increasing the equipment turn-on time. For example, a slow rate of applying voltage might be damaging to many types of electrical equipment and motors.
As a consequence of high turn-on current problems associated with the simultaneous turning on of several pieces of electrical equipment, it is usually preferable to turn on just one piece of equipment at a time, with the interval between the turning on of successive pieces of equipment being sufficient to assure that the current drawn by one piece of equipment has dropped from its high turn-on level to its normal operating level before the next piece of equipment is turned on. The following of such a time delay turn-on procedure generally permits several pieces of electrical equipment to be operated from a single building circuit without overloading the circuit.
However, the manual turn-on sequencing of several pieces of equipment is, itself, generally unsatisfactory. This is because the required time interval between the successive turn-ons is difficult to manually control. Also it may be necessary or desirable to always follow the same, predetermined turn-on sequence for a particular system of interacting electrical equipment. The following of a predetermined specific turn-on sequence may be difficult to assure by manual turn-on procedures, and out-of-sequence equipment turn-ons may cause system malfunctions, for example, loss of data in a computer system.
Because of such high current turn-on problems, specialized power controller equipment has been developed which typically provide both an instantaneous power output and a single time delayed power output or time delayed output signal. If, however, multiple time delays are required, as is the case with computer systems having a main frame computer and two or more data storage disc drives, it has been necessary to cascade two or more of the available power controllers in such a manner that one power controller provides a time delayed signal to another power controller to start its operation, and so on.
Several disadvantages are, however, associated with the use of such cascaded power controllers. For example, the use of several independent power controllers is expensive and the several power controllers require the use of often limited rack space. Also there is the problem of maintaining the several power controllers in the proper operating relationship relative to one another; particularly if any of the power controllers are temporarily disconnected for servicing. Still further, an excessive amount of equipment interwiring is required which may, in and of itself, result in electrical malfunctions or reduced operational reliability. Still further, each of the power controllers requires its own power source and the building wiring may not provide sufficient electrical outlets to accommodate the various power controllers.
To the knowledge of the present inventors, a multi-time delayed power controller has not, heretofore, been available. One reason for such availability is believed to be the difficulty in providing multiple internal delays to power outlets in a single, economical power controller.
For these and other reasons, a need exists for time delay power controllers with two or more internal delays and which provide two or more delayed power outputs capable of powering other electrical equipment.